Receiver circuit-arrangement for low-frequency or carrier wave telephony systems



' Feb. 7, 1950 J. ENSINK 2,496,784

RECEIVER CIRCUIT-ARRANGEMENT FOR LOW-FREQUENCY 0R CARRIER WAVE TELEPHONY SYSTEMS Filed Jan. 2a, 1948 JOHANNESENSJNK.

E INVENTOR.

BY%M

AGEZVI.

Patented F eb. 7,1950

UN IT EiD ,"PATENT OFFICE 2,496,784 RECEIVE JI UI ARRANGEMENT FOR LOWgEREQUENCY R CARRIER WAVE. "TELEPHONY :sYs'rEMs Johannes f; Ensink, Eindhoven, Netherlands, "as- -.=signor.'to-Hartf0rd National Bank and Trust Company,"Hartford, Conn., as trustee Al plicati'ondanuary 23,1948, Serial No. 3,964

ln -theNetherlands February 21, 1947 0 As is well-known;in=telephonyzsystems not-only speech currents, which maybe-understoodtoinclude music, but also dialling and calling signals and the like 'arerequiredto- :be transmitted.

At the transmittrend these" 1 signals have the character of direct current impulses, but incarrier-wave telephony systems and also in lowfrequency systems, *in' which transmission is effected through pupini'sedTcables, are converted into alternating current-impulses, teach impulse being built up from a' numbernf periods 0f a lowfrequency 'or high-frequency "oscillation, then they are transmitted. Attheirec'eiverend these impulses must "bore-"converted intodirect current impulses.

The invention relates'to "a receiver circuitarrangement for low fre'quency or: carrier-wave systems for amplifying low-i-freqnenc'y speech currents and for receivingsignalling impulses having a frequency'in the speech frequency band."

In the present case the transmitted impulses are consequently built (whom a number 'of' periods of an oscillation, -tne' rrequency or which -is included in the speech -freq-uncy band cry: for example, from 300 to 3000 'c/s and "is, fo'r *example 2500 c/s.

These signal-ling impulses inust *therefore- *be separated at the receiver end froin speech cun rents to Wit in such 'manner "asto prevent signalling impulses 'from inducing "interference "in the transmitted conversation and, on'the "other hand, oscillations of 2500 c/s in thes'pee'ch currents from inducin'g interference in-signalling.

- In an arrangement acc'ording to the invention, the incoming'signalis fedto theinput circuitof a discharge tube,'from=' the output circuitof-vvhich the speech currents'are abstractedpthis output circuit has coupled to it'a circuit tuned to the frequency of the-signalling' impulsesand a circuit including a rectifier'and connected in series therewith aparallel combination of a resistance and a capacity, the 'voltagesset rip-across the tuned circuit and across the parallel-combination being combined in such ma'n'ne'r and being supplied in such manner to' a'seco'n'd rectifier'with l which is connected 'in's'eriesase'cond parallel 'com- *bination of a resista'nce- 'a'nd acapa'clty, which combination is included in the; input circuit of the discharge tube, that on reception-of signalling'impuls'es a relay whi'ch-controls a signal current circuit and which -is included in the 'outut circuit of the tubepec'omes iipei-ative.

In order that the invention ma be -m'ore "clearly understoodand readily carriedi-into effect, itwill now be described nioresfu-llywith reference' to the alternative, may becombined 'to form a' single transformer comprising one primary and two secondary windings, the-output circuit of the pentode 4 hasin addition-coupledto it-the-cir- -cuit 8 tuned toithe-singalling impulses, for example to 2500 c/s, and the rectifier circuit 9.

Upon supply of asignalling impulse to the input terminals I, '2,'a'high alternatingvoltage'is set up across the circuit 8 and a direct voltage having a polarity as shown in the drawing is set up across the parallel-combination of resistance I0 and capacity l I.

These voltages are combined and supplied through rectifier l2 to'the parallel-combination of resistance l3 and capacity l4 includedin the input circuit, the voltage across the parallelcombination l0, ll having a blocking "efiect on the rectifier l2 so that the latter only allows current to pass, if a signalling impulse is fed' to the input'terminals l,'2 with the result that the circuit 8 has set up across it a voltage which exceeds the blocking voltage. Supply of voltages of speech currents having'a frequency different from 2500 0/5 results in a blocking voltage and'if 'oc casionally a speech-current frequency of 2500 "MS cccurs, the'condenser=lI is charged comparatively rapidly byway of the'small re'sistanceof the rectifier and the voltage across the tuned circuit has not yet been exhausted to the required higher voltage.

On reception of 'a'signalling impulse the parallel-combination l3, M'has setup across it a voltage of the polarity indicated in the drawing. Consequently. the discharge tubeis substantially cut off, owing to which'the direct current in the output circuit is decreased to 'the' extent-of the signalling relay i5 inclu'dedin this circuit "and controlling the signal-current circuit being deenergized and this enables a 'direct current impulse to be set up in the said signal current circuit.

Termination of the signalling impulse results .:.in damping of theoscillation'across'the circuit 8, so that the voltage across this circuit is decreased whilst with properly chosen time-constant of the parallel-combination in, II, for example 50 milliseconds the cut-oif voltage subsists for some more time. In contradistinction to this the time-constant of the parallel-combination 3, I4 is chosen to be small, for example 2 msec. so that the voltage occurring across is decreased very rapidly, with the result that the pentode 4- is again ready for amplifying speech current signals.

In a favourable form of the circuit-arrangement according to the invention the input circuit of the discharge tube has set up across it a negative bias voltage which is taken from a capacity to which the voltage set up across a resistance included in the cathode lead of the discharge tube is fed through a rectifier which is cut-off on reception of signalling impulses.

The negative bias voltage is taken from the capacity I1. This is charged with the aid of the voltage set up across the resistance which is included in the cathode lead and with which a small part I! of the potentiometer connected to the source of supply voltage is connected in series.

As long as signalling impulses do not occur, there is set up by the anode-direct anode current of the tube 4 across the resistance IS a voltage drop which exceeds the voltage across the resistance l9, which voltage has a blocking effect. The capacity I! is then charged by way of the rectifier 20. On reception of signalling impulses at which the direct anode current is very small, the rectifier is blocked.

This generated negative bias voltage has the eifect of substantially obviating any variation in value of the anode current on replacement or change of the discharge tubes.

It is well to note that the generated negative bias voltage should preferably not change upon the occurrence of signalling impulses, so that the time-constant of the network used for producing these voltages should exceed the time period of the longest impulse that occurs of the order of 400 msec.

In this case the usual parallel-combination of resistance and capacity cannot be used, since this requires either a high capacity value, which is undesirable in view of the space available in telephony receivers, or involves the use of a high resistance value.

The latter requirement is also undesirable, since the secondary electron-emission which is always evolved by the control-grid may have the effect of setting up a positive control-grid voltage, whilst the control-grid circuit already comprises a comparatively heavy resistance l3.

Thus the circuit-arrangement shown ensures that in the conductive direction of the rectifier when the latter exhibits an internal resistance of the order of magnitude of 10,000 9 a positive gridcurrent will not occur and in the other direction,

- when the internal resistance is of the order of nal pulses formed by oscillations whose frequency lies within the audio range, said system comprising an electron discharge tube including a cathode, a grid and an anode, means coupled to said grid for applying the audio currents and the si nal pulses thereto, means coupled to said anode for deriving amplified audio currents therefrom, a resonant network coupled to said anode and tuned to the frequency of said signal pulses, a first resistance-capacitance parallel circuit, a first rectifier, means coupling said first circuit through said first rectifier to said anode to charge said first circuit, a second resistancecapacitance parallel circuit, a second rectifier, means connecting said resonant network in series with said first circuit through said second rectifier across said second circuit to charge said second circuit solely when an oscillatory voltage is developed across said resonant network, means to apply the voltage developed across said second circuit to said grid to render said tube non-conductive during the existence of signal pulses, and means coupled to said anode and responsive to the non-conduction of said tube to produce output signal impulses in accordance with said input signal pulses.

2. A telephone receiving system for selectively amplifying audio currents and intercepting signal pulses formed by oscillations whose frequency lies within the audio range, said system comprising an electron discharge amplifying tube including a cathode, a grid and an anode, an input circuit coupled to said grid for applying the audio currents and the signal pulses thereto, an output circuit coupled to said anode for deriving amplified audio currents therefrom, a resonant network coupled to said output circuit and tuned to the frequency of said signal pulses, a first blocking voltage resistance-capacitance parallel circuit connected in series with said resonant network, a first rectifier, means coupling said first blocking voltage circuit through said first rectifier to said output circuit to charge said first blocking voltage circuit, a second blocking voltage resistance-capacitance parallel circuit, asecond rectifier,means connecting said serially-connected resonant network and said first circuit through said second rectifier across said second blocking voltage circuit to charge said second blocking voltage circuit solely when an oscillatory voltage is developed across said resonant network, means to apply the voltage developed across said second blocking voltage circuit to said input circuit to render said tube non-conductive during the existence of signal pulses, and means coupled to said output circuit and responsive to the non-conduction of said tube to produce output signal impulses in accordance with said input signal pulses.

3. A telephone receiving system for selectively amplifying audio currents and intercepting signal pulses formed by oscillations whose frequency lies within the audio range, said system comprising an electron discharge tube including a cathode, a grid and an anode, an input circuit coupled to said grid, means to apply said audio currents and said signal pulses to said input circuit, an output circuit coupled to said anode, a signal relay having an energizing winding, first and second coupling transformers each having a primary and a secondary, means to apply an anode potential through said output circuit in series with said relay winding and the primaries of said first and-second coupling transformers to said anode whereby said relay is energized during the conduction of said tube, a condenser connected in parallel with the secondary of said first transformer to define therewith a resonant network tuned to the frequency of said signal pulses, a first resistance-capacitance parallel circuit, a first rectifier connected in series with said first circuit across the secondary of said second coupling transformer, said first circuit and said resonant circuit being connected in series, a second resistance-capacitance parallel circuit, a sec ond rectifier, and means to connect said seriallyconnected resonant network and said first circuit through said second rectifier across said second circuit, said first circuit applying a bias across said second rectifier which is overcome by the oscillatory voltage developed across said resonant network solely during the existence of signal pulses to charge said second circuit, and means to apply the voltage developed across said second circuit to said input circuit to render said tube non-conductive during the existence of signal pulses, thereby to deenergize said relay.

4. A telephone receiving system for selectively amplifying audio currents and intercepting signal pulses formed by oscillations whose frequency lies within the audio range, said system comprising an electron discharge amplifying tube including a cathode, a grid and an anode, an input transformer having a primary and a secondary one end of which is connected to said grid, means to apply said audio currents and said signal pulses to the primary of said input transformer, an output transformer having a primary one end of which is connected to said anode and a secondary, a signal relay having an energizing winding, first and second coupling transformers each having a primary and a secondary, means to apply an anode potential to the other end of the primary of said output transformer through said relay winding in series with the primaries of said first and second. coupling transformers whereby said relay is energized during the conduction of said tube, a condenser connected in parallel with the secondary of said first transformer to define therewith a resonant network tuned to the frequency of said signal pulses, a first blocking voltage resistance-capacitance parallel circuit, a first rectifier connected in series with said blocking voltage circuit across the secondary of said second coupling transformer, said first blocking voltage circuit and said resonant circuit being connected in series, a second blocking voltage resistance-capacitance parallel circuit having one terminal thereof connected to .the other end of the secondary of said input transformer and the other terminal thereof coupled to said cathode, a second rectifier, and means to connect said serially-connected resonant network and first blocking voltage circuit through said second rectifier across said second blocking voltage circuit, said first blocking voltage circuit applying a bias across said second rectifier which is overcome by the oscillatory voltage developed across said resonant network solely during the existence of signal pulses to charge said second blocking voltage circuit thereby to apply a cut-off bias to said tube and deenergize said relay in the anode circuit thereof.

5. A telephone receiving system for selectively amplifying audio currents and intercepting signal pulses formed by oscillations whose frequency lies within the audio range, said system comprising an electron discharge amplifying tube including a cathode, a grid and an anode, an input transformer having a primary and a secondary, one end of which is connected to said grid, means to apply said audio currents and said signal pulses to the primary of said input transformer, an output transformer having a primary one end of which is connected to said anode and a secondary, a signal relay having an energizing winding, first and second coupling transformers each having a primary and a secondary, a source of anode potential having the positive terminal thereof connected to the other end of the primary of said output transformer through said relay winding in series with the primaries of said first and second coupling transformers whereby said relay is energized during the conduction of said tube, a condenser connected in parallel with the secondary of said first transformer to define therewith a resonant network tuned to the frequency of said signal pulses, a first blocking Voltage resistance-capacitance parallel circuit, a first rectifier connected in series with said blocking voltage circuit across the secondary of said second coupling transformer, said first blocking voltage circuit and said resonant circuit being connected in series, a second blocking voltage resistancecapacitance parallel circuit having one terminal thereof connected to the other end of the secondary of said input transformer, a capacitor connecting the other terminal of said second circuit to said cathode, a second rectifier, means to connect said serially-connected resonant network and first blocking voltage circuit through said second rectifier across said second blocking voltage circuit, said first blocking voltage circuit applying a bias across said second rectifier which is overcome by the oscillatory voltage developed across said resonant network solely during the existence of signal pulses to charge said second blocking voltage circuit thereby to apply a cutoff bias to said tube and deenergize said relay, a resistor connected between the negative terminal of said source and said cathode, and a third rectifier connected between said other terminal of said second blocking network and an intermediate point in said source, the voltage developed.

across said resistor during the conduction of said tube to charge said capacitor through said third rectifier being cut off on reception of signal pulses.

JOHANNES ENSINK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,958,166 Laurent May 8, 1934 2,018,464 Nibel Oct. 22, 1935 2,145,053 Meszar M Jan. 24, 1939 2,164,185 Bertnolli June 27, 1939 2,199,179 Koch Apr. 30, 1940 2,251,958 Skillman Aug. 12, 1941 2,265,203 Six Dec. 9, 1941 2,282,405 Herrick May 12, 1942 2,319,306 Dickieson May 18, 1943 2,366,011 Donaldson Dec. 26, 1944 

